JPH07113643A - Piezoelectric vibrational angular velocity meter - Google Patents

Abstract

PURPOSE:To obtain a small-sized velocity meter, which can be mass-produced at low cost, by forming a vibrator in the shape of a beam supported on both ends by a base body. CONSTITUTION:A lower electrode 4 is divided into an electrode 9 for driving and electrodes 8a, 8b for detection. When an upper electrode 6 is used as a common ground and an electric field having frequency close to the cantilever natural frequency of a vibrator 1 is applied to the electrode 9, cantilever vibrations are excited in the direction of V by the vibrations of a PZT piezoelectric film 5. When the vibrator 1 is moved in the direction V at velocity V, Coriolis force Fc works on the vibrator 1 when rotational angular velocity OMEGA is applied around the axis of a cantilever in the axial direction of the cantilever. The force deflects the vibrator 1 in the direction perpendicular to the direction of vibrations. When force is applied in the directions of OMEGA and Fc, compressive stress works on the electrode 8a side and tensile stress to the electrode 8b side. When voltage between the electrode 8a and a ground is represented by Va and voltage between the electrode 8b and the ground by Vb, a signal resulting from cantilever vibrations is offset in a signal by Coriolis force when difference Va-V2b of both voltage is taken, and only the signal by Coriolis force can be read.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric vibrating angular velocity meter for detecting a rotational angular velocity of vibration by utilizing forward and reverse piezoelectric effects. In particular, it relates to a piezoelectric vibrating angular velocity meter that is small and can be mass-produced at low cost.

[0002]

2. Description of the Related Art Piezoelectric vibrating angular velocimeters utilizing the positive and negative piezoelectric effects have conventionally been GE type and Watson type. In the GE type piezoelectric vibrating angular velocity meter, as shown in FIG. 3, a piezoelectric ceramic plate is adhered to a rod-shaped vibrator made of metal to drive the metal vibrator, and the Coriolis force generated by the rotation of the vibrator is generated. To detect. The mode of vibration used is unrestrained lateral vibration, which is usually fixed to the substrate at the node of vibration.

In the Watson type piezoelectric vibrating angular velocity meter, four piezoelectric ceramic bimorphs are used as shown in FIG.
Overlapping tuning forks are formed so that they are orthogonal to each other, the entire tuning fork is excited by the driving bimorph, and the Coriolis force generated with the rotation of the element is detected by the detecting bimorph. These elements are applied as angular velocity sensors, camera shake sensors, etc. and have a lot of achievements.

[0004]

However, in these piezoelectric vibrating gyroscopes, the structure and fixing method of the vibrator are complicated, and complicated steps such as adhesion of ceramic plates and attachment of lead wires are indispensable. Therefore, it has been impossible to reduce the size and cost. An object of the present invention is to solve these problems and provide a piezoelectric vibrating angular velocity meter that is small in size and can be mass-produced at low cost.

[0005]

According to the present invention, it is possible to combine the silicon processing process with the recently popular vapor phase synthesis method of piezoelectric / electrostrictive materials as a means for producing a piezoelectric vibrating gyro. Based on the idea, a vibrator is formed on a silicon substrate that is a base by a silicon processing process, and a thin film made of a piezoelectric / electrostrictive material is formed on the vibrator by a method that matches the silicon processing process. The shape is a cantilever beam or a double-supported beam supported by a substrate.

[0006]

[Function] When a thin film made of piezoelectric / electrostrictive material is applied with an AC electric field having a frequency close to the resonance frequency of the lateral vibration of a cantilever beam type or a doubly supported beam type oscillator made of silicon, vibration occurs due to the piezoelectric inverse effect The natural vibration is excited in the child. When rotation occurs around the beam axis at this stage, Coriolis force is generated in a direction perpendicular to both the beam axial direction and the vibration direction. This force deforms the beam in the direction perpendicular to the vibration caused by the driving electric field, and if the induced charge generated by the piezoelectric positive effect is detected in another piezoelectric / electrostrictive thin film fixed to the vibrator by this,
The rotational angular velocity can be estimated by the following relationship.

F _c = 2 m [v · Ω] (1) where F _c is the Coriolis force, m is the mass of the vibrator, v is the vibration speed of the vibrator, and Ω is the rotational angular speed. The thin film made of a piezoelectric / electrostrictive material formed directly on the vibrator or through another layer such as an electrode is preferably formed by a method compatible with the silicon processing process, for example, sputtering, vacuum deposition, It is formed by a vacuum thin film forming technique such as EB vapor deposition and MOCVD.

The silicon processing process typified by photolithography and anisotropic chemical etching is basically a two-dimensional processing process. Therefore, in order to make the cost particularly low, the shape of a vibrator that can be two-dimensionally processed is used. Is desirable, for this purpose, a thin film made of piezoelectric / electrostrictive material,
Further, it is desirable that electrodes for taking out the piezoelectric effect from this thin film are formed parallel to the surface of the silicon wafer.

From the detection electrode, in addition to the piezoelectric signal caused by the Coriolis force, an output obtained by adding the piezoelectric signal associated with the vibration of the beam is obtained. When Coriolis force is applied, the beam bends in the direction perpendicular to the vibration direction, and compressive stress is applied to one side and tensile stress is applied to the other side symmetrically with respect to the center plane of the beam. Here, if the detection electrodes are arranged symmetrically with respect to the central axis of the beam, the piezoelectric signals due to the Coriolis force obtained from both electrodes have the same absolute value and opposite signs. Since the piezoelectric signal based on the vibration of the beam is the same at both electrodes, only the signal due to the Coriolis force can be obtained by taking the difference between the outputs obtained from both electrodes.

In order to further simplify the element, instead of separately forming the driving / detecting piezoelectric / electrostrictive thin films, separate electrodes are attached to one piezoelectric / electrostrictive thin film. It is desirable to use a part of the film for driving and another part for detecting.

[0011]

The present invention will be described in more detail with reference to the following examples. FIG. 1-1 shows an example of the piezoelectric vibrating gyro according to the present invention. A cantilever type oscillator (1) made of silicon is fixed to the same silicon substrate (2).
A silicon nitride film (3) is formed on the silicon upper surface, and a platinum lower electrode (4) and lead zirconate titanate (P) are formed on the silicon nitride film (3).
A ZT) piezoelectric film (5) and a platinum upper electrode (6) are formed. FIG. 1-2 is a view of the element as seen from above cut along the surface of the platinum lower electrode.

The lower electrode is for driving (9) and for detecting (8a,
It is divided into 3 parts of b). When the upper electrode is used as a common ground and an electric field having a frequency close to the cantilever natural frequency of the vibrator is applied to the driving electrode, the cantilever vibration is generated in the direction indicated by V in the figure by the vibration of the PZT piezoelectric film. Be excited. When the oscillator is moving in the direction of V at velocity V,
When a rotational angular velocity Ω is applied around this axis in the axial direction of the cantilever, the Coriolis force F _c acts on the oscillator according to the above-mentioned formula (1). This force causes the oscillator to flex in a direction perpendicular to the direction of vibration. When a force is applied in the direction shown in FIG. 1-2, compressive stress acts on the detection electrode 8a side and tensile stress acts on the detection electrode 8b side. _Let v _a be the voltage detected between the detection electrode 8 a and the ground, and v _b be the voltage detected between the detection electrode 8 b and the ground, then v _a , v _b
In addition, in addition to the signal associated with the Coriolis force, the signal resulting from the cantilever vibration is detected in a combined form. Since the signals due to the Coriolis force have different signs in v _a and v _b , the difference v _a −v _b between the two
If is taken, the signal due to the cantilever vibration is canceled out, and only the signal due to the Coriolis force can be read.

FIG. 2 shows an example of a manufacturing process of the piezoelectric vibration angular velocity meter shown in FIG. A silicon nitride film is formed on both surfaces of a Si (110) wafer by a CVD method, and then a Pt / Ti film to be a lower electrode is formed on one surface by a sputtering method (2-1). Next, a three-divided electrode pattern to be a drive and detection electrode,
At the same time, a resist pattern corresponding to the necessary lead portion and wiring bonding portion is formed by photolithography (2-2). Further, the Pt / Ti film is removed by reactive etching except the part covered with the resist pattern until the underlying silicon nitride film is reached (2
-3). Then, a resist is formed by photolithography except for a portion which becomes a void necessary for forming the cantilever and a portion which corresponds to a boundary between elements (2-4). Similarly, silicon nitride corresponding to voids is removed by reactive etching (2-5). Similarly, a resist pattern is formed on the back surface, leaving a portion corresponding to the void (2-
6) Then, the silicon nitride film is removed by reactive etching in this portion (2-7). When the entire silicon wafer processed in this way is anisotropically etched with potassium hydroxide, the etching proceeds from a portion without silicon nitride serving as a protective film against etching to obtain a cantilever shape (2
-8). Next, a PZT thin film is formed on a portion centered on the cantilever by a sputtering method (2-9). Finally, the upper electrode is formed by mask vapor deposition to complete the device (2-1
0). By connecting an appropriate driving power supply and a detection circuit to this element, it can be used as a piezoelectric vibration angular velocity meter.

With respect to the doubly supported beam type piezoelectric vibration angular velocity meter,
The manufacturing process and operating principle are basically the same as those of the cantilever type.

[0015]

As described above, according to the present invention, an extremely small and inexpensive piezoelectric vibrating angular velocity meter can be obtained.
The piezoelectric vibrating angular velocity meter of the present invention can be used not only as a single unit but also as a small system such as a micromachine or a microrobot.

[Brief description of drawings]

FIG. 1 is an example of a piezoelectric vibrating angular velocity meter according to the present invention.

FIG. 2 is an example of a process for manufacturing the piezoelectric vibration gyro shown in FIG.

FIG. 3 is a conceptual diagram of a conventional piezoelectric vibration angular velocity meter.

FIG. 4 is a conceptual diagram of a conventional piezoelectric vibration angular velocity meter.

[Explanation of symbols]

 1 oscillator 2 substrate 3 silicon nitride 4 lower electrode 5 PZT film 6 upper electrode 7 silicon nitride film (substrate) 8 detection electrode 9 drive electrode 10 resist 11 cutting groove 12 PZT 13 metal oscillator 14 drive piezoelectric ceramic plate 15 Piezoelectric Ceramic Plate for Detection 16 Piezoelectric Ceramic Bimorph for Driving 17 Piezoelectric Ceramic Bimorph for Detection

Claims (5)

[Claims] 1. A vibrator and a substrate that supports the vibrator formed by a silicon processing process, and a thin film made of a piezoelectric and / or electrostrictive material formed on the vibrator directly or through another layer. A piezoelectric vibrating angular velocity meter, wherein the vibrator has a doubly supported beam shape supported by the base body. 2. A vibrator formed by a silicon processing process, a substrate supporting the vibrator, and a thin film made of a piezoelectric and / or electrostrictive material formed on the vibrator directly or through another layer. A piezoelectric vibrating angular velocity meter, wherein the vibrating element has a cantilever shape supported by the base body. 3. The piezoelectric vibrating gyro according to claim 1, wherein a thin film made of the piezoelectric and / or electrostrictive material is parallel to the vibrator with electrodes on both sides of the thin film. A piezoelectric vibrating gyro characterized by being formed. 4. The piezoelectric vibration angular velocity meter according to claim 3, wherein at least one of the electrodes formed on both surfaces of the thin film is divided into two symmetrically with respect to the axis of the beam, and signals obtained from both electrodes are divided. A piezoelectric vibrating angular velocity meter characterized by detecting a piezoelectric signal resulting from Coriolis force by taking a difference. 5. The piezoelectric vibration angular velocity meter according to claim 3, wherein at least one of the electrodes formed on both surfaces of the thin film is divided into three symmetrically with respect to the axis of the beam, and the central electrode portion is for driving. A piezoelectric vibrating angular velocity meter characterized in that the electrode portions on both sides are for detection, and the difference between the signals obtained from both detection electrodes is taken to detect the piezoelectric signal due to the Coriolis force.